In modern fuel supply systems, water separators are usually employed in the associated fuel filter devices in order to lower as far as possible a water proportion contained in the fuel. If the water contained in the fuel is not separated, undesirable corrosion, abrasion, material embrittlement and cavitation can result in the following units. An increased water proportion in the fuel supply system likewise leads to a growth promotion of micro-organisms, which bring about sliming-up of the fuel filter device and can caused increased corrosion on the filter housing. As water separators, so-called coalescers are usually employed, which coalesce minutest water proportions into larger water droplets, separating these out of the fuel-water emulsion because of the gravity. Insofar as necessary for the water separation, a so-called end separator consisting of a hydrophobic fabric can filter out the water drops contained in the fuel-water emulsion. The water separated in this manner is then collected in separate water collection spaces, from which it is drained periodically or when replacing a filter element at the latest.
From DE 10 2010 062 813 A1 a filter device for an internal combustion engine of a motor vehicle, in particular a fuel or lubricant filter, with a filter housing and a ring filter element arranged in the same flowed through in radial direction from a raw side to a clean side. On the clean side of the filter element and below the same, a water separator is arranged here, which comprises a hydrophobic annular membrane extending in axial direction of the filter element that is permeable for fuel/lubricant from radially outside to radially inside. This is a classic coalescer which is to improve the degree of water separation. Disadvantageous with the water separators known from the prior art is that these only have a limited lifespan, the efficiency towards the end of the lifespan in part decreases substantially and should therefore be for example periodically replaced.